Process and product for coating molds and cores



Patented Mar. 14, 1933 UNITED STATES PATENT OFFICE PROCESS AND PRODUCTFOR COATING HOLDS AND GORES No Drawing.

Application filed February l'l, 1930. Serial No. 429,228.

(GRANTED UNDERTHE ACT OF EAIIGH 3, 1883, ASAMENDED APRII. 30, 1928 3700. G. 757) My invention relates to a new and useful method of makingmolds and cores for metal castings. v

Previously in this art the hot metal coming in contact with the mold andcore surfaces caused the sand in contact to burn into the adjacentsurfaces of the metal and produced castings-of rough exterior andinterior surfaces, which surfaces are formed of an inte- 10 gral film ofmixed metal and sand. This, as

well as the removal of the cores and the cleaning of the un-integralsand from ,the casting, has heretofore been an expensive, laborious anddusty task freqiie-ntly requiring the use of pneumatic chisels and othertools, while in the machining of such castings the integral film of sandand metal is diilicult to machine unless the tool in its first cut yondthe depth of such film.

have been produced due to hard cores and molds which do not crushreadily as the metal casting cools, contracts and solidifies, and suchcastings are a constant source of substan- ?5 tial loss in all foundriesbut more especially in aluminum and kindred metal castings.

A further. constant source of substantial loss in the prior art of metalcasting has resulted from mold and core blows due to the lowpermeability of the sand forming such molds and cores.

The oxidizing of the surfaces of castings, especially of the moreoxidizing metals, due to contact with the prior art molds and cores hasmany disadvantages.

In the past many endeavors have been made to overcome these veryobjectionable 'conditions and losses. Some of these attempts have beento form the molds and cores of green 40 sand, which is the ordinarymolding sand of commerce, but the liability of such molds and cores tobe washed in part into the molten flowing metal being cast prevents, orrenders hazardous, their use in many cases.

strength than possessed by green sand molds and cores, it heretofore hasbeen common practice to embody a binder in the sand of, either or all,clay, molasses and water, flour and water, and oil, and to indurate suchmolds penetrates be-' In the prior art many cracked castings To providemolds andcorcs of more and cores by baking. Such molds and cores haveall the aforesald defects except the tendency to wash into the flowingmolten metal While the thus formed harder molds and cores increase thecracking liability of the castings as well as tend to increase theliabili-v ty of the castings to blow due to the lesser porosity of suchmolds and cores. r

Heretofore volatile substances have been i employed in and about thefoundry in the molding and core rooms, for instancein applying the sameto the mold or core'as a whole orto the surfaces thereof and thenignited to dry the mold sufiiciently before the molten metal was casttherein or thereabout; but such a practice adds a very substantial firehazard and explosion hazard. Furthermore, such volatiles becomeimpregnated in the air,

' breathed by the operatives, which tend to harmfully affect theoperatives physically 7'0 and in their efficiency. My present inventionrelates to an improved method and means for foundry practice. Its objectis to overcome the aforesaid conditions, to cheaply and readily producea mold or core of as great,and even greater, strength, durability andpermeability than normal strength,'to produce a mold or core which maybe used advantageously at very later periods of time than is possiblewith molds or cores of the prior art.

To attain these and other objects, and in accordance with the generalfeatures of this unitary invention of related and interdependentcomponents, my improvedmethod contemplates the employment of latex. Thissubstance is the natural rubber substantially as it comes from theplant, usually with the addition of a preservative, and which normallycontains a substantial water content. In some 90 rubber growing regionsthe water content of p I the latex is reduced substantially byevaporationin order to avoid the substantial shipping cost of the watercontent. i

This material, instead of being mixed with the sand or otherconstituents of the mold and/or core, as my companion applicationlikewise entitled and executed under the same date herewith, is appliedupon the surfaces of the molds and/0r cores which may come in contactwith the casting being cast. This application may be by brushing,spraying, or otherwise applying this material to such surfaces of themold and/ or core after the same have been made pursuant to the priorart. This material so applied penetrates into the surfaces to which thesame has been applied to a depth proportionate to the amount so appliedto a given surface. In penetrating into the surfaces to which the sameis applied more or less of the rubber or rubber-like content of thematerial is carried beneath the surface to which the same is applied andmore firmly binds the particles of the mold and/or core in contact withsaid material. Thus, when the impregnated surfaces become dry theparticles thereof are more firmly bound together by this rubber orrubber-like material so applied to and penetrating such surfaces. Thismay be said to substantially case harden the surfaces of the mold and/orcore adapted to come in contact with the casting when being made.

As the latex is coated upon the surfaces of the mold and/or core itpenetrates to a substantial extent. In such penetration, the sand orother content so penetrated tends in some respects to act as a filterand cause a larger proportion of the solids to be deposited upon or nearthe surface to which the same was applied and the depositing of aproportionately lesser extent of said solids in the deeper penetration.This obtains a further binding of the particles at and near the outersurfaces so that the same are stronger and more resistant to deformationby handling, erosion by the casting or otherwise. This conditionprogressively decreases substantially throughout the depth of saidpenetration into such surfaces, until the point is reached where thepenetration terminates, from which point the remainder of the mold and/or core may be of the consistency and strength normal in the prior art.This substantial progression substantially tends to prevent any tendencyto peel or scale off the coated surface.

An eflicient coating of the latex upon the mold and/ or core surfaces aswell as the said penetration thereof, by mixing with the latex asuitable protective colloid such as gelatin, agar agar, glue, sodiumsoap and ammonium soap, extract of quince seed, and the like, watersoluble substances. Such colloids added to the latex reduces the surfacetension of the water content of the latex and of the solid contained inthe latex and liquid, which colloid holds said solids more effectivelyand efficiently in suspension as well as increases the permeability ofthis mixture into the surfaces of the mold and/or core to which the sameis applied.

The amount of the protective colloid to be added to the latex dependsupon the extent desired of the penetration of the normal solidconstituents of the latex into the surfaces to which the same areapplied, while some of the colloids which may be employed also tend toincrease the binding eflect of the mixture upon the constituents of themold and/or core surfaces to which same are supplied.

It is further contemplated that the latex mixture above stated may beemployed with or without the addition of any of the welllcnownvulcanizing ingredients. When such vulcanizing ingredients are added,they may be either of the atmospheric or the artificial air curing orheat curing variety. Where the air curing variety may be applied, themold or core is subjected to atmospheric conditions for a sufficientperiod to vulcanize the sand, and where the heat curing vulcanizingagent is employed, the mold or core is subjected to the requisiteelevated temperature to cure the same to the degree of strength requiredby each particular mold or core or class thereof. During suchvulcanizing period, or during the period between the making and theusing of the unvulcanized molds or cores, the surfaces thereof havetheir moisture contents reduced by evaporation.

The mold or core thus produced is then used in the making of a casting,most usually by having the molten metal poured thereon or thereabout.Where molten metal is poured into or about the mold or core, itsheatcoming in contact with the surfaces of the molds and/or cores causes agas to be formed which permeates the cavity in the mold to be occupiedby the molten metal. This gas is in direct contact with the surfaces ofthe metal in the mold and through which gas the metal is being poured oris otherwise maintained in intimate contact with said gas. As the metalis poured into the molds this gas attains a pressure in the mold cavitybut such pressure is higher between the molten metal and the surface orsurfaces of the mold covered thereby. This gas pressure causes the moldor core to become more or less permeated by said gas. This permeationtends to filter or condense, either or both, from the gas theconstituents thereof and to deposit the same upon the walls of the moldor core. This gas and/or said filtration or condensation product prev ntthe sand or other earthy constituents of the mold or core from becomingembedded into or adhering to the surfaces of the casting when made witha mold or core in the practice of my method.

This result is also contributed to by the fact that the heat of themolten metal applied to the surfaces of the mold and/or core tends todecompose some or all of the said materials coated upon the sand andupon other earthy content of the mold or core. This decomposition inwhole or in part tends to form a protective, insulating or other coatingor medium intermediate the juxtaposed surfaces of the molten metal andthe mold g adhering to the surfaces of the casting.

I My method also substantially .reduces of practically eliminates thetendency'toward oxidization of the surfaces of the cast metal.

My method further substantially decreases the normal tendency of themetal surfaces of 5 earthy particles the casting in contact with themold, par-, ticularly iron castings and the like, from peeling orhardening and thus making thin castings more brittle and all castingssuriaces more difiicult to, machine than heretoore. The aforesaid stepsmay alsobe said to be included in, or 'to comprise the method of,slowing up the cooling rate of the-castings made in or about suchmold-or cores and which substantially contributes to the avoid ance ofsaid brittleness of thin iron castings and the machining difficulties ofother iron castings, and which also substantially contributes to theprevention of the earthy par ticles of the mold or core from beingembedded intoor adhering to the surfaces of the casting. This latterresult iscontributed to by the formation of an insulated gas film beweenthe juxtaposed surfaces of the casting and the mold or core and/or thedecomposition in whole or in part upon the surfaces of the mold or coreof some one-or more of the aforesaid ingredients coated upon the themold or core. T

Castings of all kinds, and more especially of molten metal, made in thepractice of my method may be cleaned at a fraction of the -cleaningcostf required by the practices of To demonstrate the practical utilityof my said method, I employ a mold and/or core constructed in accordancewith my said method and have made and caused to be mademany kinds ofcastings in such molds and/or cores of many'different kindsof metals andtheir. alloys and other *cast substances.

' Instead of the employment of latex as above described the practice ofmy method may be advantageously accomplished by the employment of latexembodying the parti cles or a rubber solution that had been vulcanizedto the desired degree or the employment of artificial latex and/orrubber or rubber-like dispersions and/or the product or products oflatex, rubber, or rubber-like substances indispersion or otherwise,including such substances or the rubber base thereof, as may have beentreatedby another substance such, for instance, as a sulphonic acid,

a halogen, or, a substance which may have modified some of theproperties which ordinarilycharacterize rubber'or rubber-likesubstances. The amount of the latex rubber or forming the main body of'vated temperature. K It is to be understood that wherever 1nrubber-like substance or the derivative thereof employed in the practiceof my method depends upon the degree of strength required in the moldand/or core required for the eflicient production of a cas ing of 'givencharacteristics. For instance, molds and/or cores having relatively thinareas which are more liable to crumble or be broken off in normalhandling or production, or to wash into the fluid material being castshould have greater strength. Such greater strength may be obtainedatwill by the employment of a greater percentage of a more concentratedsolution, a variation of the ingredients of the mixture, including thepossible increment of the amount of accelerant of vulcanization, or theincrement of the period or rate of the curing or vulcanization of themold and/or core, which those having skill in the art may readilydetermine from the' characteristics of the desired casting and/or thecharacteristics of themetal, alloy or substance to be cast.

This greater strength may be afforded any particular part, area, orportion of the mold and/0r core by applying to each such part,

area, or portion more of my said coating. This may be done all at oneoperation or the coating may be applied uniformly and then subsequentlyincreased at thepoint or points desired.

Inthe attainance of molds and/or cores of greater strength, where theaforesaid substance or substances employed therefor may i in any caseresult in the constituents of the mold or core becoming too moist for advantageous construction of the mold or core therefrom, which conditionis readily recognizable by those skilled in the art, the excess moisturemay be readily removed therefrom by an of the practices. employed in theart, inclu ingvits being subjected to normal atmospheric or an elevatedtemperature.

, In this specification and its appended claims where the term rubber isemployed it is, intended to include rubber either as latex, coagulatedrubber, rubber dispersions, artificial latex, orsap from trees such as He'vea brazzliensz's, or from vines or shrubs, as well as from otherkindred vegetation such as guayule containing 'more or less rubberhydrocarbon. The rubber may be unvulcanized or consist of vulcanizedsoft rubber, and may have been previous l this specification and itsappended claims the y subjected to an eleexpression rubber-like is used,it is to inelude only materials which are like. rubber in that theyafford substantially the same reaction as the rubber to the heat of thecast 3' metal, and which reaction is new and-unexpected in this art.- Itmay also include any rubber orscrap rubber, either or ooth,

that has been subjected to. an elevated tem-' perature/aloneor 1n thepresence of sulphuric acid or a sulphonic acid or a sulphonyl halide orit may also include a substance such as is an article of commerce underthe name Thermoprene. It may alsoinclude dispersions of one or more ofsaid substances. Wherever the prior art permits, the terms rubber andrubber-like are to be construed as referring to substantially the samematerial or composition., A number of the foregoing materials comewithin the ,heat plastic grouping. number of the before statedmaterials, including those subjected to the action of sulphuric acid,.or a sulphonic acid or a sulphonyl halide, and the stated Thermopreneand the like, fall within the less chemical unsaturation than rubbergrouping, the heat plastic grouping, and the rubber. isomer groupings Inthis art, coatings, binders or paste for application to cores and moldsare recognized compositions of commerce used in the production of moldsand cores for the making of castings of molten metal.

In the development of my present invention I have made or caused to bemade many molds and/or cores for different types of castings ofdifferent metals, compositions, or materials, and I have coated thesame, separately and in combination, the various materials hereinbeforestated, and have attained satisfactory results in substantially allrespects therewith.

In this art, binders for the constituents of molds and cores arerecognized articles of commerce exclusively used in the production ofmolds and cores only forthe making of castings of hot metal.

The molds and/or cores made in accordance with my invention are notrequired, as

in the prior art, to be used soon after their production nor are theyrequired to be handled with the care of such production of the priorart, and that the molds and/or cores produced in accordance with mymethod possess substantially greater strength and equal or superiorpermeability and may be used in forming a casting at a remote periodafter their production.

The material with which they are coated tends to prevent the absorptionof moisture by the molds and/or cores and hence does not require thecare with respect to moisture proof storage nor as to the humidity oftheir surrounding atmosphere as do molds and/or cores of the prior art.

While the ingredients which I employ in coating the molds and/or coresare higher in cost than the mold and/or core binders of the prior art,yet the percentageof such 'materials added-to the mold and/or corematerial is ively small even with castings requiring. greatest strengthof mold and/or core he difference in the cost of my binding materials isvery much less than the saving which their use entails even in the oneitem of the cleaning cost of the castings, This renders the use of mymethod and means profitable even in the one item of casting A cal in theproduction of molds and/or cores of large areas than in my aforesaidaccompanying application because in the present application thesubstances coated to the desired extent and quantity only beneathsurface or surfaces of the mold and/or core to come in contact with thecasting, whereas in said accompanying application, my binder is mixedthroughout the sand or other ingredient of the body of the mold and/orcore, or a substantial portion thereof.

This invention is in furtherance and continuance of, and an improvementupon, the invention set forth in my pending application likewiseentitled and bearing Serial No. 382,226.

I have found it advantageous in the production of molds and or cores forcertain types of castings to construct the mold and/ or core inaccordance with my aforesaid accompanying application and then to coatthe surfaces thereof or some portion or portions thereof as hereinstated to attain a greater strength of such coated surfaces or portionsthereof.

I have obtained satisfactory results by mixing with the hydrated rubberor rubber-like mixture a substantial amount of solids in the form ofsmall particles of graphite or other facing material, the amount of suchfacing material added being interdependent upon either or both thepercentage of other solids in the rubber or rubber-like mixture or therequired strength of the mold or core; the object being to lessen theamount of the rubber or rubberi like material employed, which is usuallythe most expensive constituent, and yet not to so lessen to the degreeof unduly weakening the resulting mold or core. material further tendsto control the amount of gas formed by the hot metal against thesurfaces of the mold or core by lessening substantially to the extent ofthe added facing material the rubber or rubber-like material that isdecomposed by the heat of the metal.

The invention herein described may be manufactured and used by or forthe Government of the United States for governmental purposes withoutthe payment to me of any royalty thereon or therefor.

Having now so fully described my invention that others skilled in theart may there- Such added facing from make and use the same, what Iclaim and components, tempering same,- making the v mold or core,coating one or more surfaces of the mold or core with a hydrated rubbermixture, and dehydrating said coating to the desired extent.

2. The method of producing molds or cores including the step of coatingone 01' more surfaces of the mold or core with a hydrated rubbermixture.

3. The method of producing molds 01' cores consisting of selecting themolding sand or components, tempering same, making the mold or core,coating one or more surfaces of the mold or core with a hydrated rubbermixture containing an added colloid, and dehydrating said coating to thedesired extent.

4. The method of producing molds or cores including the step of coatingone or more surfaces of the mold or core with a hydrated rubber mixturecontaining an added colloid.

5. The method of producing molds or cores including the step of coatingone or more surfaces of the molds or cores, with a hydrated mixturecontaining a substance selected from the class of artificial and naturalrubber and derivatives thereof, and an added colloid.

6. The method of producing molds or cores consisting of selecting themolding sand or components, tempering same, making the mold or core,coating one or more surfaces of the mold or corewith a hydrated rubbermixture containing a facing material, and

dehydrating said coating to the desired extent.

7. The method of producing molds or cores including the step of coatingone or moresurfaces of the mold or core with a hydrated rubber mixturecontaining a facing material.

8. The method of producing molds or cores consisting of selecting themolding sand or components, tempering same, making the mold or core,coating-one or more surfaces of the mold or core with a hydrated rubbermixture containing a facing material and an added colloid, anddehydrating said coating to the desired extent.

9. The method of producing molds or cores including the step of coatingone 'or more surfaces of the mold or core with a hydrated rubber mixturecontaining a facing material and an added colloid.

10. The method of producing molds or cores including the step of coatingone or more surfaces of the mold or core with a mixture containingsubstantially hydrated rubber, a facing material, and a colloid selectedfrom the class of Water soluble colloids.

11. The method of producing molds or cores including the step of coatingone or more surfaces of the mold or core with a mixture containingsubstantially hydrated rubber in small particles, a facing material insmall particles, and an added colloid selected from the class ofadhesive colloids.

12. A mold or core having a coating containing hydrated rubber.

13. A mold or core having a coating conizaining hydrated rubber mixedwith a coloid.

- 14. A mold or core having a coating containing hydrated rubber and afacing material.

15. A mold or core having a coating containing substantially hydratedrubber, and a graphite facing material.

16. A mold or core having a coating containing hydrated rubber mixedwith a col loid and a facing material.

. 17.. A mold or core having a surface adapted to be subjected to moltenmetal, said surface having associated therewith substantially hydratedrubber mixed with a colloid and a graphite facing material.

18. The method of casting in a mold comprising the steps of pouringmolten metal in a mold, and by the heat of said poured metal combustingsubstantially hydrated rubber between the metal and the mold surfaces.

19. A coating, hinder or paste (for molds and cores for making moltenmetal castings) comprising a suspension containing an adhesive binderselected from the class comprising substantially natural and artificialrubber and a derivative thereof, and a colloid selected from the classcomprising substantially gelatin, agar agar, glue, sodium soap, ammoniumsoap, and extract of quince seed.

20. A coating, binder or paste (for molds and cores for making moltenmetal castings) comprising a suspension containing an adhesive binderselected from the class comprising substantially natural and artificialrubher and a derivative thereof, a facing material in small particles,and a colloid selected from the class comprising substantially gelatin,agar agar, glue, sodium soap, ammonium soap, and extract of quince seed.

21. A mold or core coating, hinder or paste, comprising dispersions ofrubber and a facing material suspended in a liquid containing a colloid.

CHARLES MARSHALL SAEGER, J R.

